It’ll definitely happen, but it remains to be seen whether people will actually stay. For all we know, this latest Twitter thing could be resolved this week and people will come crawling back because they’ve built up a network/following there. Something like that is really hard to destroy, and even then I think it’s far more likely that a commercial product with a large budget and fancy apps takes in most of the users.
I also feel like the Twitter brand is still too well known to die forever. Even if it goes away for a while, someone else will buy it and bring it back.